The invention refers to a device for purifying waste water of the type described in the preamble of claim 1.
A method of this type is known from EP 0 170 332 B1. The known device operates anaerobic, preferably according to the UASB method (upflow anaerobe sludge blanket) in which a container is used in whose lower portion the waste water to be purified is conducted and from whose upper portion the purified water is let off. Anaerobic micro organisms are active in the container. Stacked gas collectors in the form of hoods are located in the waste water inlet and the overflow for the purified water. The upper portion of the hoods is connected to a gas-sludge separation means via a line. The action of the micro organisms generates gas, which settles down on the sludge so that this sludge floats towards the top as so-called scum. This scum is caught by the hood and gradually emits its gas so that it becomes heavier and sinks back to the ground as so-called sinking sludge. The gas emitted by the pellets rises together with the free gas bubbles caught by the hoods towards the top in the lines and thereby entrains scum particles and fluid that was separated in the gas-sludge separation chamber. The gas is purposefully carried away while the fluid entrained, which may also contain sludge particles, reaches a penstock, which leads back to the bottom of the container. The purified waste water reaches a discharge line in the upper portion of the container via an overflow and is drawn off there. However, it proved that the purification power of such containers still needs to be improved.
Thus, the invention is based on the object of providing a method and a device for purifying waste water by means of which the purification effect is optimized in a constructively simple manner.
The object is solved by the features cited in claim 1. By the method according to the invention of again sucking on medium from the upper portion of the container and introducing it into the purification circle, a circulation of the medium in the container is started or enforced, which leads to a substantially improved purification effect, wherein by the utilization of the gas lifting effect of the already separated gas, this improved purification effect neither requires energy nor complicated constructive modifications for instance in already existing containers.
In a useful manner, the medium taken-in is conducted back into the container together with those ingredients of the medium that were entrained during the gas accumulation.
Claim 3 describes an especially preferred device for carrying out the method according to the invention.
To realize the improved purification effect according to the invention, only one additional line exists between the upper portion of the container and the gas collection line which can of course also easily be retrofit in already existing containers.
Advantageous embodiments of the device according to the invention can be derived from subclaims 4 to 10.